Super-Superbugs: Antibiotic-Resistant Bacteria May Be Deadlier

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Antibiotic-resistant bacteria may be tougher superbugs than
previously thought: Not only are these bacteria harder to treat,
they appear to be "fitter" in general, meaning they survive
better in the host and cause more deadly infections, a new study
suggests.

The findings go against the prevailing view in medicine that when
bacteria acquire resistance to drugs, they become less "fit" in
some way, for example, they spread less easily. Although
scientists have assumed this is true, evidence supporting this
view is limited, the researchers said.

They found that mice infected with antibiotic-resistant strains
of P. aeruginosa were more likely to die (without any
type of treatment) during the study period than mice infected
with P. aeruginosa strains that did not have antibiotic
resistance. [ 6
Superbugs to Watch Out For ]

The antibiotic-resistant strains were also better able to kill
certain immune
cells (the body's defenses against bacteria and other
pathogens).

"A potentially overlooked consequence of the acquisition of
antimicrobial resistance could be enhanced fitness and virulence
of pathogens," wrote the researchers from Brigham and Women's
Hospital in Boston in today's (July 22) issue of the journal
Science Translational Medicine. The finding "raises a serious
concern that drug-resistant strains might be better fit to cause
serious, more difficult to treat infections, beyond just the
issues raised by the complexity of antibiotic treatment," they
said.

The researchers also had similar findings for two other strains
of bacteria: Acinetobacter baumannii, which causes
infections in people in hospitals, and Vibrio cholera,
which causes the
diarrheal disease cholera. For example, V. cholera
bacteria with certain genes for antibiotic resistance were better
able to grow in the gastrointestinal tracts of rabbits than
bacteria without these genes.

"Our results show that efforts to confront the worldwide increase
in antibiotic resistance might be exacerbated by fitness
advantages that enhance virulence in drug-resistant microbes,"
the researchers wrote.

The findings also "emphasize the necessity to effectively control
the emergence of antibiotic-resistantpathogens as well as the
development of alternative approaches to prevent and treat
infections," they wrote.

Dr. Amesh Adalja, an infectious-disease specialist and a senior
associate at the University of Pittsburgh Medical Center's Center
for Health Security, said the new findings were not completely
surprising. That's because mutations that allow bacteria to
resist certain antibiotics can have other effects as well,
including boosting the bacteria's ability to survive. "It's not
just a simple trade-off," between genes for antibiotic resistance
and pathogen fitness, said Adalja, who was not involved in the
study.

Adalja also noted that researchers have discovered bacteria in
caves that are resistant to many antibiotics, even though these
bacteria have never had contact with humans, or been exposed to
antibiotic drugs. Bacteria likely evolved to have these
resistance genes a long time ago, to defend themselves against
other bacteria, or help them survive in other ways, Adalja said.

"Antibiotics resistance isn’t just something that happened after
the discovery of penicillin," Adalja said.

The findings show that there may always be some level of
antibiotic resistance, even if doctors improve the way they use
antibiotics. "There may be limits to what antibiotic stewardship
can do," Adalja said.

This means
stopping antibiotic resistance will require more than just
judicious use of antibiotic, Adalja said. Researchers need to
develop treatments and prevention methods that work in ways that
are different from antibiotics, such as drugs that target certain
bacterial toxins, or new vaccines, Adalja
said.